1. Technical Field
The present invention relates to a liquid droplet ejection head, and in particular to a liquid droplet ejection head that ejects droplets of high viscosity ink.
2. Related Art
In liquid droplet ejection devices of currently marketed water-based ink jet printers, dye inks and pigments inks are used with a viscosity generally around 5 cps, and of the order of 10 cps at the most. It is known that printing ability can be improved by increasing ink viscosity, in order to prevent ink bleeding on impact with the printing medium, to increase the optical color density, and to reduce the amount of water contained therein so that swelling due to wetting of the medium can be suppressed and drying times can be reduced, or in order to increase the degrees of freedom in the overall design of such high quality inks.
However, a high powered pressure generation mechanism is required to eject high viscosity liquids, leading to detrimental effects on the cost, an increase in head size and the like.
The present inventors have previously submitted patent applications for liquid droplet ejection heads that impart compression and rotational movement to a beam and that use a sudden up-down movement when a buckling direction is reversed to separate by inertia a high viscosity liquid from a nozzle in the desired direction.
However, a tail of, for example, in excess of 1 mm is drawn out from a liquid droplet during ejection when a high viscosity liquid is ejected. In some cases the length of this tail becomes longer than the throw distance of the ejection head, and there are occasions when a tail is drawn out so as to bridge between the head and medium printed on. Consequently the impact shape of the liquid droplet is not a centrally symmetrical circular shape, but is shaped like a tadpole. In addition there is the problem that the tail remains after impact of the liquid droplet on the medium, delaying the stabilization of the meniscus on the nozzle surface, resulting in delays to the refilling of the nozzle, thereby impeding high frequency ejection.
As a result of investigating the above problems, the present inventors have discovered that by applying a voltage/difference in electrical potential between the head and a medium in a head for high viscosity liquid ejection, electricity is conducted through the drawn out tail portion, this being an effective method for heating the tail of the liquid droplet and positively and selectively severing the tail from the liquid droplet.